Discharge reaction mechanism of room-temperature sodium-sulfur battery with tetra ethylene glycol dimethyl ether liquid electrolyte

Abstract

The first discharge curve of a sodium-sulfur cell using a tetra ethylene glycol dimethyl ether liquid electrolyte at room temperature shows two different regions: a sloping region and a plateau region of 1.66V. The first discharge capacity is 538 mAhg(-1) sulfur and then decreases with repeated charge-discharge cycling to give 240 mAh g(-1) after ten cycles. Elemental sulfur of the cathode changes to sodium polysul-fides Na2S2 and Na2S3,during full discharge. The sodium polysulfides, however, do not reduce completely to elemental sulfur after full charging. In summary, the mechanism of the battery with liquid electrolyte is 2Na + nS -> Na2Sn(4 > n >= 2) on discharge and Na2Sn(4 > n >= 2) -> x(2Na + nS)+ (1 -x)Na2Sn(5 > n > 2) on charge. (C) 2011 Elsevier B.V. All rights reserved.